When substrates are reactively processed in a vacuum, as is the case—for example—in semiconductor production, it is customary to employ a plasma produced in the vacuum chamber of a vacuum recipient for a multitude of process steps, cases in point being the possibly reactive coating or the possibly reactive etching of a substrate.
In this connection it is known that the plasma can be produced by inductive and/or capacitative means.
EP 0 271 341 A1, for example, describes a device for the dry etching of semiconductor disks that comprises an induction coil for plasma production and an electrode device for extracting ionized particles from the plasma onto the substrate. In the device described in U.S. Pat. No. 6,068,784, again, energy for plasma production is inductively coupled into the vacuum chamber of the vacuum recipient by means of a coil-type antenna, the vacuum chamber in this case serving as reactor. The substrate is situated on an electrode that serves as substrate carrier and to which there is applied a so-called RF (radio frequency) bias or polarizing potential.
U.S. Pat. No. 5,460,707 describes a device for capacitative plasma production that can also be used for coating purposes. A magnetic field—produced by an additional permanent or electromagnet—may be provided in this case for controlling the plasma density distribution or producing a locally greater plasma density.
When substrates are subjected to vacuum processing, as is the case—for example—in semiconductor production, it is very important to have an extremely uniform plasma density distribution over the entire surface of the substrate in order to assure an appropriately uniform substrate processing. To this end it is essential to screen or compensate all disturbing external influences, especially external fields.
Although, for example, it is theoretically possible to use a ferromagnetic shell to screen the vacuum recipient, this is rather disadvantageous from a practical point of view, because such a shell would considerably increase the weight of the vacuum recipient. Furthermore, it would become more difficult to gain access to the vacuum recipient whenever maintenance or repair work has to be carried out.
EP 0 413 283 teaches that a planar plasma can be obtained by means of an electrically conductive planar pancake coil, the induction field being produced by connecting a high-frequency voltage source to the pancake coil and coupled in through a dielectric screening.
U.S. Pat. No. 6,022,460 suggests that a further magnetic field—produced by a pair of Helmholtz coils—should be allowed to act on the plasma, which can be inductively produced (or at least co-produced), for example, by means of either a pancake coil to which there is applied a high-frequency alternating voltage or a coil in the form of a vacuum bell. Applied to the pair of Helmholtz coils is a direct and alternating current combination such as to produce a weak magnetic field that is modulated by the alternating current component, said modulation being described as a “shaking” of the magnetic field”. According to the patent in question, this serves essentially to obtain an increase of the plasma density and an improvement of the uniformity of the plasma.
One drawback of the device for the production of a plasma described in U.S. Pat. No. 6,022,460 consists of the fact that the additional pair of Helmholtz coils makes it more difficult to obtain a compact design and also increases the cost of the device. Since considerations of high-frequency technology require the induction coil to be decoupled from the pair of Helmholtz coils, it is absolutely essential that the induction coil should be spatially separated from the Helmholtz coils.
The present invention therefore sets out to make available a procedure and a device for the production of a high-density plasma that would either avoid the described drawbacks associated with the state of the art or be affected by them only to a lesser extent. Further tasks of the present invention will be brought out by the detailed description thereof given hereinbelow.